1. Field of the Invention
The present invention relates generally to stairways, and more particularly to a circular stairway and method for manufacture thereof wherein one or more flights of stairs are attached to and supported by a helical newel cut from a rigid tube or cylinder.
2. Description of the Prior Art
Previously, curved stairways have either been spiral or circular. Spiral stairways typically have the treads attached to either a solid or hollow cylinder, column or newel of relatively small diameter. As a consequence, the inner run of the treads is normally very narrow, resulting in a significant risk of tripping or slipping to a lower stair. Most spiral stairways involve modular construction of some or all of the stairway, including the supporting newel, treads, and in some cases even a spiral-shaped outer stringer. Patents disclosing modular spiral stair construction include McCloud U.S. Pat. No. 4,850,164 for "Multi-Unit Stair Construction and Method" which discloses the use of a narrow inner column with modular attachments; Rorke U.S. Pat. No. 4,587,780 for a spiral staircase having a perforated narrow inner column for tread attachments; Morellini U.S. Pat. No. 4,527,367 entitled "Spiral Staircase" combines a narrow modular center column and treads; Gerlach U.S. Pat. No. 4,413,460 discloses use of a narrow two-piece center column; Sanders U.S. Pat. No. 4,338,751 teaches the use of a narrow modular center column; Takenaga et al. U.S. Pat. No. 4,190,992 provides a narrow inner column with modular attachments; and Brauckmann et al. Swiss Patent No. 560,305.
When the center column is made with a larger diameter, more visibility up and down the stairway usually results, and the stairway is usually referred to as a "circular" stairway. Circular stairways have been used since the Middle Ages as a means of providing passage from one floor level to another. Typical constructions included spanning stairs between a rounded central wall and an outer wall, somewhat like that illustrated in WIPO Publication WO92/03625; cantilevering of the stairs from a central newel post, like that disclosed in U.S. Pat. No. 415,078 to Wagner; cantilevering the stairs from a cylindrical outer wall; supporting the stairs on one or more helically formed stringers, as illustrated in the patents to Krstovic (U.S. Pat. No. 5,058,339) and Benedetti (U.S. Pat. No. 4,918,799).
While reducing some of the problems associated with the narrow inner tread runs and poor visibility of spiral staircases, circular stairways normally require complex construction for structural support. As disclosed in Benedetti and Krstovic, the additional structural support is provided by formed stringers affixed to both inner and outer ends of each tread. The forming of the stringers obviously necessitates additional labor and alignment, and often requires the use of complex tools and jigs to hold and align the stringer materials as they are formed. Krstovic suggests that traditionally constructed circular stairways may even require additional structural supports in the form of cross-bracing between the stringers.
There is thus a need for a circular stairway design having a radius of curvature such that the inner run of the treads is wide enough to step upon without risk of slipping to a lower stair, and having an open configuration so as not to block visibility up and down the staircase. There is also a need for a simpler and less expensive method of making circular stairs.